CN111747352A

CN111747352A - Lifting device supported by two-wheeled automatic guided vehicle

Info

Publication number: CN111747352A
Application number: CN202010228283.0A
Authority: CN
Inventors: A·科兹洛诺克
Original assignee: Approaching Robot Co ltd
Current assignee: Magna New Travel Usa
Priority date: 2019-03-29
Filing date: 2020-03-27
Publication date: 2020-10-09
Anticipated expiration: 2040-03-27
Also published as: GB201904413D0; US20200307973A1; CN111747352B; GB2582649A; US11608254B2; GB2582649B; EP3715314A1

Abstract

A mobile lift device having a platform coupled to an elongated lift arm arranged in a crossed configuration by a hinge at a central portion of the lift arm, which enables the lift arm to rotate in a cross-scissor fashion as the platform is raised or lowered. The lower ends of the lift arms are coupled to automated guided vehicles that move toward each other to raise the platform and away from each other to lower the platform. Actuating a locking mechanism coupled to the lift arm to prevent the lift arm from moving and thereby locking the height of the platform.

Description

Lifting device supported by two-wheeled automatic guided vehicle

Technical Field

The technical field of the application is the physical operation of technical flow, product design and assembly optimization in robotized manufacturing.

Background

Scissor lift devices have been used to raise and lower platforms. A scissor lift may have lift arms arranged in a crossed configuration with a hinge coupled to a central portion of the lift arms. The upper end of the lift arm may be coupled to the platform and the lower end of the lift arm may be coupled to a single unitary movable structure having wheels. An actuator coupled to the lift arm is used to move the lift arm between a more horizontal orientation and a more vertical orientation. When the lift arm is in the horizontal orientation, the platform is lowered, and when the lift arm is in the vertical orientation, the platform is raised.

A common disadvantage of existing scissor lift devices is that they require an additional dedicated lift mechanism to move the lift arms and raise the platform. The lift mechanism may be a hydraulic or electric motor that is incorporated into a linear actuator in an Automated Guided Vehicle (AGV) design. The lift mechanism is an additional structure that requires power and maintenance. There is a need for a simplified lifting device that does not require a dedicated lifting mechanism.

Disclosure of Invention

A mobile lift device has a platform coupled to an elongated lift arm that raises and lowers the platform. Both AGVs are controlled by an AGV controller to move the mobile lift device to any destination. The raising and lowering of the platform is based on the distance between the two AGVs. The two AGVs may be coupled to a lift arm that supports the platform centerline. The AGV may have a swivelling coupling extending from an upper surface of the AGV to a lifting arm. The upper end of the lift arm may be coupled to a lower surface of the platform. For example, the upper end of the first lifting arm may be coupled to a hinge fixed to an end of the platform, and the upper ends of the second and third lifting arms may be coupled to a sliding mechanism on the opposite side of the platform. The slide allows the upper ends of the second and third lift arms to move inwardly toward the centerline when the platform is raised and outwardly when the platform is lowered.

The lift arms may be arranged in a cross pattern with an upper end of a first lift arm coupled to a hinge on one end of the platform and upper ends of a second lift arm and a third lift arm coupled to a second end of the platform, the second end being on an opposite side of the first end. The central portion of the lift arm is coupled to a hinge that allows the lift arm to rotate in a cross-scissor fashion when the platform is raised or lowered. A locking mechanism may be attached to the lift arm to prevent the platform from accidentally falling in the event of a power failure or AGV control failure. In one embodiment, the locking mechanism may be attached to a central hinge portion of the lifting arm. In another embodiment, the locking mechanism may be attached to the slider to prevent the upper ends of the second and third lifting arms from moving.

Drawings

FIG. 1 shows a perspective view of the lifting platform on two AGVs.

FIG. 2 shows a side view of the lift platform in a raised position on two AGVs.

FIG. 3 shows a side view of the lift platform in a lowered position on two AGVs.

FIG. 4 shows a side view of the lift platform in a lowered position and a raised position on two AGVs.

Fig. 5 shows a perspective view of a lifting arm with a locking mechanism.

FIG. 6 shows a side view of the lift platform with locking mechanism in a partially raised position on two AGVs.

Fig. 7 shows a bottom view of a track with a locking mechanism.

FIG. 8 shows a perspective view of the lifting platform on four AGVs.

FIG. 9 illustrates a front view of the attachment mechanism on the AGV.

Detailed Description

Fig. 1 shows a lower perspective view of an embodiment of a mobile lift device 101, the mobile lift device 101 having a platform 103, the platform 103 coupled to

elongated lift arms

111, 113, 121, the

lift arms

111, 113, 121 raising and lowering the platform 103. In this example, the

lift arms

111, 113, 121 are arranged in a cross pattern, with the upper end of the first lift arm 121 coupled to a hinge on one end of the platform 103, and the upper ends of the second and

third lift arms

111, 113 coupled to a second end of the platform 103, the second end being on the opposite side of the first end. The second and third lifting

arms

111 and 113 are parallel to each other, and the first lifting arm 121 may be located between the second and third lifting

arms

111 and 113. The central portions of the

lift arms

111, 113, 121 are coupled to an arm hinge 131, the arm hinge 131 allowing the first lift arm 121 to rotate about the arm hinge 131 with respect to the second lift arm 111 and the third lift arm 113.

In the example shown, the upper end of the first lifting arm 121 is coupled to an upper hinge 115, the upper hinge 115 allowing the first lifting arm 121 to rotate relative to the platform 103. The lower end of the lift arm 121 is coupled to a first lower hinge 129, the first lower hinge 129 allowing the first lift arm 121 to rotate about a horizontal axis relative to the first AGV 127. The lower ends of the second and

third lift arms

111, 113 are connected to a second lower hinge 119, the second lower hinge 119 allowing the second and

third lift arms

111, 113 to rotate about a horizontal axis relative to the second AGV 117. A vertical coupling (coupling) in the first AGV127 allows the first lift arm 121 and the first lower hinge 129 to rotate about a vertical axis relative to the first AGV 127. The vertical coupling in the second AGV117 allows the second and

third lift arms

111 and 113 to rotate about a vertical axis relative to the second AGV 117. In an alternative embodiment, the third lift arm 113 is parallel to the first lift arm 121, rather than parallel to the second lift arm 111, and the upper end of the third lift arm 113 is coupled to the hinge 115 at the lower front of the platform 103 and the third lower end is coupled to the first AGV 127.

The upper ends of the second 111 and third 113 lift arms are coupled to a slide 125, the slide 125 sliding within a track 126 extending along a portion of the length of the platform 103. The slider 125 is coupled to upper ends of the second and

third lift arms

111 and 113. The rail 126 may securely hold the slider 125 and the upper ends of the second and

third lift arms

111 and 113 at the bottom of the platform 103. In one embodiment, the track 126 may have two "C" section rails (rails) located on opposite outer sides of the slide 125, the slide 125 moving within the track 126, which prevents the slide 125 from vertically separating from the platform 103.

The slide 125 moves within the track 126 and may have various designs. In another embodiment, the slider 125 may have a surface made of a low friction material, such as teflon, Delrin, or other lubricious polymeric material, that slides against the track 126. In other embodiments, the slider 125 may have wheels, bearings, or bushings that roll against the track 126 with a low friction movement. In other embodiments, any other sliding mechanism may be used to couple the upper ends of the second and

third lift arms

111, 113 to the platform 103 and allow the described movement.

The mobile lift 101 is supported by a robot with two separate wheels, which may be an Automatic Guided Vehicle (AGV)117, 127, the AGVs 117, 127 operating independently and not rigidly coupled to each other. In the example shown, the AGVs 117, 127 may each have two wheels 363 that are each driven by a motor 353. In one embodiment, the motor 353 may be a brushless direct current (BLDC) motor. The motor 353 is powered by a rechargeable battery and controlled by a motor controller. The motor controller may include a main controller circuit and an electric power switching mechanism. The motor controller may include a general purpose Central Processing Unit (CPU), such as an Arduino controller, and a general purpose input/output (GPIO) installed driver. For other equipment mounted on the mobile lift 101 (e.g., lift locks, cameras, sensors, etc.), the CPU may also act as a control unit.

The AGV may also include wireless network communications. For example, the communication mechanism may be a Radio Frequency (RF) device, such as a Wi-Fi mechanism or any other RF communication transceiver system. These controls may be used to alter the spacing between the two AGVs used by each platform to raise and lower the platforms. In one embodiment, the system controller may send navigation control to a plurality of AGVs, and each AGV may send position information back to the system controller to feedback the position of the plurality of AGVs. To turn each AGV, one wheel may rotate faster than the opposite wheel. For example, when the left wheel rotates faster than the right wheel, the AGV will turn to the right. The AGV is free to rotate under the platform. The rear AGV may be controlled to maintain a fixed orientation and alignment with the platform (aligned with) so that the rear AGV follows the front AGV. In one embodiment, the AGV may move a payload (payload) placed on a platform to a payload load/unload position. The platform may be moved vertically to a desired height as described above, and the robotic mechanism may load or unload a payload from the platform.

Fig. 2 shows a side view of the mobile lifting device 101 in a raised platform 103 configuration. The hinges may each have an axis of rotation perpendicular to the length of the platform 103 as shown and parallel to each other. The upper ends of the second and third lifting

arms

111 and 113 are coupled to the slider. In the raised position, the upper ends of the slider, the second lift arm 111, and the third lift arm 113 move inward toward the center of the platform 103. Similarly, the AGV127 moves inward toward the center of the platform 103.

Fig. 3 shows a side view of the mobile lifting device 101 in a fully lowered platform 103 configuration. In the lowered position, the upper ends of the slider, the second lifting arm 111 and the third lifting arm 113 are moved outwardly towards one end of the platform 103. In this example, the first lift arm 121, the second lift arm 111, and the third lift arm 113 are all in horizontal and parallel directions.

Fig. 4 shows another side view of the mobile lifting device 101 showing the difference between the fully raised and fully lowered positions of the platform 103. Note that in this example, the AGV117 does not move when the platform 103 is in the raised and lowered configuration. When the platform 103 is in the lowered position, the first AGV127 and the second AGV117 are spaced apart by a distance X, which represents the maximum extended separation distance between the first AGV127 and the second AGV 117. The distance X may be a predetermined maximum separation distance. When the platform 103 is in the fully raised position, the platform 103 has a height Z and the first AGV127 and the second AGV117 are spaced apart by a distance X', which may represent a minimum separation distance.

The movement of the first AGV127 and the second AGV117 of the mobile lifting device 101 can be wirelessly controlled by the AGV controller 191. In the lowered position, the controller 191 may move the mobile lift 101 by movement of only the (leading) first AGV127 and the (following) second AGV 117. The traction force will cause the second AGV117 to separate from the first AGV127 and the separation distance is always X. When the controller 191 instructs the first AGV127 and the second AGV117 to move toward each other, the platform 103 may be raised to Z and the separation distance is X'. When the controller 191 instructs the first AGV127 and the second AGV117 to maintain an X' distance between each other, the platform 103 maintains an elevated height Z as the

AGVs

117, 127 move.

A more common control scheme for the controller 191 is to move the mobile lifting device 101 to the payload loading area with the platform 103 in the lowered position. The controller 191 may then move the

AGVs

117, 127 toward each other to raise the platform 103 to the desired height Z. The payload may be placed on the platform 103 and the controller 191 may then move the

AGVs

117, 127 away from each other to lower the platform 103 so that the mobile lift 101 can transport the payload to the destination in a lowered, more stable position. At the destination, the controller 191 may again move the

AGVs

117, 127 toward each other to raise the platform 103 to the desired height Z so that the payload may be removed from the platform 103.

Fig. 5 shows a perspective view of the first 121, second 111 and third 113 lifting arms. In this example, the upper ends of the second and

third lift arms

111, 113 are coupled to a slider 125, the slider 125 being a wheel that can roll within a track coupled to the bottom of the platform 103. The central portions of the first, second, and

third lift arms

121, 111, and 113 are coupled to a hinge 131, and the hinge 131 allows the first lift arm 121 to rotate with respect to the second and

third lift arms

111 and 113.

The locking mechanism 151 may be coupled to the first lifting arm 121, with the locking mechanism 151 extending and retracting the pin 153. When the locking mechanism 151 retracts the pin 153, the first lifting arm 121 is free to move rotationally relative to the second lifting arm 111. In the extended position, the locking mechanism 151 may extend the pin 153 and the pin 153 may pass through the hole 163 to prevent the first lifting arm 121 from rotating relative to the second lifting arm 111.

In one embodiment, the locking mechanism 151 is attached to the first lift arm 121 and a plate structure 161 having a plurality of holes 163 is coupled to the second lift arm 111. In the example shown, the plurality of holes 163 in the plate 161 may be arranged in a radial pattern, where each hole 163 has the same inner diameter and each hole 163 has the same distance to the center of rotation of the hinge 131. The plate 161 may be parallel to the second lifting arm 111. When a power failure occurs, the locking mechanism 151 may extend the pin 153; the locking mechanism 151 may retract the pin 153 when power is available and control the locking mechanism 151 to retract the pin 153. If any supporting AGV experiences a power failure, the platform supported by the first 121, second 111 and third 113 lift arms will remain in the raised position and will not collapse. Uncontrolled collapse of a platform carrying heavy objects may damage the products, lift mechanisms and/or AGVs on the platform.

The placement of the pins 153 in each of the different holes 163 may each have a different locking height of the platform 103. In this example, the highest locking platform height may be achieved when the pin 153 is inserted into the lowest hole 163. Conversely, when the pin 153 is inserted into the highest hole 163 (the hole 163 closest to the platform 103), the lowest locking platform height can be achieved. In the fully lowered position, the locking mechanism 151 does not need to place the pin 153 in the hole 163 because the platform 103 is already in the lowest position and will not fall out in the event of a power failure of the AGV.

FIG. 6 illustrates a side view of an elevator mechanism coupled to the first AGV127 and the second AGV117, which may move in conjunction with the locking mechanism 151. A particular sequence of steps may be taken to lock the platform 103 at a desired height. The locking mechanism 151 may retract the pin 153, thereby unlocking the locking mechanism 151, the first lifting arm 121 may rotate about the hinge 131 relative to the second lifting arm 111, and the platform 103 may move vertically.

The

AGVs

117, 127 may then be controlled to move the platform 103 such that the

AGVs

117, 127 move toward each other to separate them a particular distance. The controlled distance may be less than the fully lowered position and greater than the fully raised position. When the first AGV127 and the second AGV117 are separated by a distance corresponding to the target height position of the platform 103, as described, the locking mechanism 151 may extend the pin 153, and the pin 153 may pass through the aligned holes 163 and lock the height of the platform 103.

If the aperture 163 is misaligned, the distance between the

AGVs

117, 127 will need to be adjusted. In one embodiment, the locking mechanism 151 may detect when the pin 153 is extended but not yet inserted through the aperture 163. The AGV127 can respond to this by moving the AGV127 very slowly toward the AGV117 or away from the AGV117 until the pin 153 is aligned with the aperture 163 and the pin 153 is extended into the aperture 163. Once the pin 153 is inserted into the hole 163, the lift mechanism is locked, the first lift arm 121 cannot rotate about the hinge 131 with respect to the second lift arm 111, and the platform 103 does not move vertically.

The weight of the object placed on the platform 103, as well as the weight of the platform 103 itself, will cause the holes 163 to create a shear force as it attempts to remove the alignment with the position of the pins 153. Thus, to disengage the locking mechanism 151, the

AGVs

117, 127 may be controlled to move toward each other such that the first lift arm 121 and the second lift arm 111 rotate a small amount to align the pin 153 with the hole 163. As the shear force on the pin 153 is removed, the locking mechanism 151 may be actuated to retract the pin 153 from the hole 163, and then the first and second lifting

arms

121 and 111 may rotate freely.

In another embodiment, the height locking mechanism 171 can be coupled to the rail 126, and a series of holes 177 can be formed in the sides of the rail 126. The locking mechanism 171 may be coupled to a series of spring-loaded pins 175, with the pins 175 aligned with each hole 177. When the locking mechanism 171 is in the unlocked configuration, the pins 175 are fully retracted, and the slider 125 is free to move within the track 126, the first lift arm 121 may rotate about the hinge 131 relative to the second lift arm 111. When the locking mechanism 171 is in the locked configuration, the pin 175 enters the track 126 through the unobstructed aperture 177. The pin 175 aligned with the slide 125 does not enter the track 126. However, the pin 175 will enter the track 126 on the opposite side of the slider 125 and prevent the slider 125 from moving in the track 126. The inserted pin 175 will also prevent the first lift arm from rotating about the hinge relative to the second lift arm, which will also prevent the platform 103 from moving vertically. When power is available, the locking mechanism 171 may be in the locked or unlocked configuration, and when power is not available, the locking mechanism 171 is in the locked configuration.

Although the arrangement has been described as having two AGVs mounted below the centerline of the platform, in other embodiments, as shown in FIG. 8, four or more AGVs 117, 127 may be used in a parallel configuration under a larger platform 104, which may increase platform stability. The platform 104 may be rectangular or square in shape, and the

AGVs

117, 127 may be roughly positioned at each corner of the square or rectangular platform 104. The

AGVs

117, 127 may be arranged such that the

lift arms

111, 113, 121 of the lift mechanism may be substantially parallel to each other. The

AGVs

117, 127 may be controlled such that the opposing elevator mechanisms may operate in a coordinated manner (in a coordinated manner) to simultaneously raise and lower both sides of the platform 104 at the same rate so that the platform 104 is always parallel to the ground as it moves in a vertical direction. In one embodiment, a sensor such as an accelerometer may be mounted on the platform to measure the horizontal alignment of the platform. If an alignment error is detected, the

AGVs

117, 127 may be adjusted to correct the alignment error. Once the lift mechanism raises the platform 104 to a desired height, the locking mechanism may be engaged, thereby simply maintaining planar alignment of the platform 104.

FIG. 9 illustrates a front cross-sectional view of an embodiment of an AGV127 with a first lift arm 121 coupled to a first AGV hinge 129. The shaft 130 may extend through a lower end of the first lift arm 121 and define a horizontal rotational axis. The first AGV hinge 129 may be coupled to a vertical shaft 217, and the vertical shaft 217 may rotate about a vertical axis at the top of the AGV 127. The shaft 217 may be a cylindrical structure having a cylindrical outer surface that extends downward into a head tube 203, the head tube 203 being coupled to an upper central portion of the AGV. In the illustrated embodiment, the head pipe 203 may be coupled to the frame of the AGV.

Bearings are installed in the head pipe 203 to allow the shaft 217 to rotate smoothly. In one embodiment, an upper radial bearing 207 is mounted within the upper cylindrical surface of the head tube 203 and a lower thrust bearing 205 is mounted within the upper cylindrical surface of the head tube 203. The outer diameter of the upper radial bearing 207 may be substantially the same as the inner diameter of the upper cylindrical surface of the head tube 203, and the outer diameter of the lower thrust bearing 205 may be substantially the same as the inner diameter of the lower cylindrical surface of the head tube 203.

A holder cup 213 is installed in the upper radial bearing 207 and the lower thrust bearing 205. The holder barrel 213 may have an upper cylindrical surface and a lower cylindrical surface. The outer diameter of the upper cylindrical surface of the holder cylinder 213 may be substantially the same as the inner diameter of the upper radial bearing 207, and the outer diameter of the lower cylindrical surface of the holder cylinder 213 may be substantially the same as the inner diameter of the lower thrust bearing 205. The locking ring 209 may be compressed and placed within the inner diameter of the head tube 203 above the upper radial bearing 207. Locking ring 209 may then be placed in a groove formed in the inner diameter of head tube 203 to retain upper radial bearing 207, cartridge 213, and lower thrust bearing 205 in head tube 203. In one embodiment, a dust shield 231 may be placed over the upper radial bearing 207 to prevent contamination of surrounding particles. A dust shield 231 may be placed against the upper portion of the holder barrel 213 in the head tube inner diameter above the upper radial bearing 207. In one embodiment, the stent barrel 213 surrounds an elastomeric (elastomer)211 having a concave cylindrical surface. A cylindrical metal shell 219 is placed in the concave cylindrical surface of the elastomer 211, the cylindrical metal shell 219 providing a sliding surface for the shaft 217 when the AGV127 is removed from the shaft 217, lift mechanism, and platform 104. The lower surface of the inner diameter of the upper radial bearing may be adjacent to the protrusion to prevent the holder cylinder 213 from being pulled up from the head tube 203 after the locking ring 209 has been installed in the head tube 203.

Although the AGV is illustrated and described as using the upper radial bearing 207 and the lower thrust bearing 205 as ball bearings, in other embodiments other rotational mechanisms may be used that allow the shaft 217 to freely rotate within the head tube 203 under axial and radial loads with low friction, such as bushings (bushing), needle bearings, roller thrust bearings, or any other mechanism.

The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, subcombinations thereof, and subsets thereof. Those skilled in the art will understand how to make and use the present invention. In various embodiments, the invention includes apparatuses and processes provided in the absence of items not depicted and/or described herein or in various embodiments, as well as apparatuses and processes provided in the absence of items that may have been used in previous apparatuses or processes (e.g., for purposes of improving performance, simplifying operation, and/or reducing cost of implementation). Rather, as the following claims reflect, inventive aspects lie in less than all features of any single foregoing disclosed embodiment.

Claims

1. A lifting device, comprising:

a platform;

a first lift arm having a first upper end coupled to a hinge at a lower surface of the platform;

a second lift arm having a second upper end coupled to a slide that moves within a track mounted on a lower surface of the platform;

a lift arm hinge coupled to a central portion of the first lift arm and the second lift arm;

a first Automatic Guided Vehicle (AGV) having a first coupling attached to a first lower end of the first lift arm; and

a second AGV having a second coupling attached to a second lower end of the second lift arm;

wherein the lifting device has a lowered configuration and a raised configuration; in the lowered configuration, the platform is lowered and the distance between the first and second couplings is maintained at a maximum predetermined distance; in the raised configuration, the platform is raised and the distance between the first and second couplers is less than the maximum predetermined distance and equal to a minimum predetermined distance.

2. The lifting device as recited in claim 1, further comprising:

a rotary coupling having a vertical axis of rotation between the first lower end of the first lift arm and the first AGV.

3. The lifting device as recited in claim 1, further comprising:

a rotary coupling having a vertical axis of rotation between the second lower end of the second lift arm and the second AGV.

4. The lifting device as claimed in claim 1, wherein the slider has:

a wheel that rolls against an inner surface of the track; or

A bearing rolling against an inner surface of the track; or

A low friction surface that slides against an inner surface of the track.

5. The lifting device as recited in claim 1, further comprising:

a third lift arm having a third upper end coupled to the hinge of the lower front of the platform and a third lower end coupled to the first AGV, wherein the third lift arm is parallel to the first lift arm.

6. The lifting device as recited in claim 1, further comprising:

a third lift arm having a third upper end coupled to the lower rear of the platform slide and a third lower end coupled to the second AGV, wherein the third lift arm is parallel to the second lift arm.

7. The lift device of claim 1, wherein the platform has a flat upper surface.

8. The lifting device as recited in claim 1, further comprising:

a controller for controlling movement of the first and second AGVs;

wherein the controller controls the first and second AGVs to move the first and second couplers toward each other to raise the platform and controls the first and second AGVs to move the first and second couplers away from each other to the maximum predetermined distance to fully lower the platform.

9. The lifting device as recited in claim 1, further comprising:

a controller for controlling movement of the first and second AGVs;

wherein the controller controls the first and second AGVs to move independently while maintaining a predetermined distance between the first and second couplings.

10. The lifting device as recited in claim 1, further comprising:

a controller for controlling movement of the first and second AGVs;

wherein the controller controls the first and second AGVs to move independently while maintaining a fixed distance between the first and second couplings less than the maximum predetermined distance.

11. The lifting device as recited in claim 1, further comprising:

a third lift arm having a third upper end coupled to a lower surface of the platform;

a fourth lift arm having a fourth upper end coupled to a second slide of a lower surface of the platform;

a second lift arm hinge coupled to a central portion of the third lift arm and the fourth lift arm;

a third automated guided vehicle AGV having a third coupling attached to a third lower end of the third lift arm; and

a fourth AGV having a fourth coupling attached to a fourth lower end of the fourth lift arm.

12. The lift device of claim 11, further comprising:

a controller for controlling movement of the first, second, third and fourth AGVs;

wherein the controller controls the first and second AGVs to maintain a fixed distance between the first and second couplers, and the controller controls the third and fourth AGVs to maintain a fixed distance between the third and fourth couplers.

13. The lifting device as recited in claim 1, further comprising:

a locking mechanism coupled to the first lift arm and the second lift arm, wherein the locking mechanism has a locked position that prevents rotation of the first lift arm relative to the second lift arm about the hinge, and the locking mechanism has an unlocked position that allows rotation of the first lift arm relative to the second lift arm about the hinge.

14. The lifting device as recited in claim 1, further comprising:

a locking mechanism coupled to the track, wherein the locking mechanism has a locked position that prevents movement of the slider and the second lift arm relative to the platform and an unlocked position that allows movement of the slider and the second lift arm relative to the platform.

15. The lift device of claim 13 or 14, wherein the locking mechanism comprises a plurality of holes and a pin, the pin being inserted through one of the plurality of holes in the locked position and the pin being retracted in the unlocked position.